• Share
  • Email
  • Embed
  • Like
  • Save
  • Private Content







Total Views
Views on SlideShare
Embed Views



0 Embeds 0

No embeds



Upload Details

Uploaded via as Adobe PDF

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
Post Comment
Edit your comment

    dotnet_remoting dotnet_remoting Document Transcript

    • 3 DotNET RemotingLecture: [Link]Tutorial (Part 1): [Link]3.1 Introduction.NET remoting is a technology which allows objects to be placed remotely across anetwork, where the object can be activated, and communicate with local objects us-ing a communications channel. A formatter is then used to encode and decode themessages as they pass between the remote object and the application. The format ofthese message can either be: Binary encoded. This is used where performance is a critical factor. XML encoded. This is used when interoperability is important, and uses the standardized SOAP protocol.A key element of .NET remoting is that objects can check the messages that are to besent before they are sent to the channel, and the remote objects are activated in dif-ferent ways, these are: Client-activated objects. These have a finite lease time, and once their lease has expired, they are deleted (using the garbage collector). Server-activated objects. These can either be defined with a single call or with a singleton. A single call accepts one request from a client, then performs the ac- tion, and is finally deleted (with the garbage collector). It is defined as stateless, as it does not hold onto parameters from previous calls. Singletons are stateful and can accept multiple calls, where they remember previous calls, and retain their information. They can thus communicate with multiple clients. Also the lifetime of singletons is controlled by lease-based lifetime.3.2 Application boundariesMicrosoft Windows allows applications to run on virtual machines, where applica-tions should not interfere with each other. Thus, a fault in one application shouldnot affect another one. Each application thus has its own code and data area, whichshould not be accessed by other applications running on the machine. A processboundary is one which isolates a process from others which are running. It is neces-sary that each process can run in its own virtual space, and gain access to as muchmemory that they require. Other processes should not be able to interfere with this.If a process crashes, it should not affect other processes. .NET expands on this byapply this managed environment onto applications. This is because .NET uses theCommon Language Runtime (CLR - Figure 3.1) which is a managed environment
    • for executing code, code access security, object management, debugging, cross-language integration, and profiling support. In standard Windows applications it isnot possible to provide a degree of safety that an application does not step outwithits boundaries, as Windows applies process control boundary, rather than an appli-cation boundary. In .NET an application domain is created with the AppDomainclass with the System namespace. Thus the application boundary ensures that: Each application has its own code, data and configuration settings. No other application can interfere with any other applications.It is thought that application switching for processor time is more efficient thanprocessor switching. Along with this, it is easier to monitor the operation of an ap-plication than it is to monitor a number of processes. VB .NET VB .NET C# C# FCL FCL (Framework (Framework CLS CLS Class Library) Compiler (Common (Common Class Library) Compiler Language Language Specification) Specification) Web Web component component CTS CTS (Common (Common MSIL (Microsoft Type Type Intermediate Language) System) System) CLR (Common Language Runtime) CLR (Common Language Runtime) Allows the programs to run – similar to the Java Virtual Machine (JVM) Allows the programs to run – similar to the Java Virtual Machine (JVM) Figure 3.1: .NET Framework3.3 Distributed SystemsDistributed systems allows resources to be distributed around a network, ratherthan tying them to a specific host. These resources could relate to hardware andsoftware resources. This allows for less centralized approach, and typically im-proves the robustness of a system and also makes improved usage of networktraffic. For example an organisation might use a centralized Web server for theirdocument management. This has the advantage is that it is relatively easy to man-age, but it becomes a centralized point of failure, also the network traffic is likely tobe relatively large towards the server. Along with this the CPU usage it likely to berelatively large. An improved system would be to distribute Web servers around the network,and for hosts to access them on a local level. This type of approach can be scaleddown to an object-level, where objects can be distributed around a network, eitheroutwith the application domain, or outwith the host. These objects could reside onW.Buchanan Unit 3 - .NET Remoting 2
    • different types of operating systems or system types and thus allow applications torun over heterogeneous systems. Another similar approach is to develop applications which is made of intercon-nected components. These components make it easier to design software, wheretasks are split into elements. The distribution of components allows for the stan-dardization of components, which could run remotely. For example a componentwhich does a grammar checker could be standardized and when an application re-quires a grammar checker it calls it up remotely, and uses it. In general distributed systems are generally more scaleable, more robust, andincrease availability of services. The most common distributed protocols are RPC(Remote Procedure Calls), Microsoft Distributed Object Model (DCOM), CommonObject Request Broker Architecture (CORBA) and Java Remote Invocation (RMI).These are typically applied to certain types of environments, such as DCOM onWindows-based systems and RPC in a UNIX environment. Some of these are legacytype systems which were designed to be simple, and have never really kept up-to-date with modern methods, especially related to security. The .NET frameworkhopes to produce a new standard for distributed applications. The main namespaces used for .NET Remoting include: System.Net. This includes classes relating to the networking elements of the dis- tributed system. System.Runtime.Remoting. This includes classes for the remote aspects of the .NET framework, such as mechanisms for remote communication between ob- jects. System.Web.Services. This includes protocols relating to Web services, such as those relating to HTTP and SOAP. This is defined as the ASP.NET Web services framework.3.4 Remote Objects.NET remoting provides a simple mechanism to call remote objects, where a remoteobject is any object which is outside the application domain, and can thus also belocal on the same machine. Within an application domain, the object is passed byreference, whereas primitive data types are passed by value. Obviously it is notpossible to pass an object from a remote object by reference since the reference to theobject is only valid on the side which contains the object (that is, they only have lo-cal significance). For an object to be passed over an application domain, they mustbe passed by value, and also serialized (that is, send over a single communicationschannel). This, thus, defines the structure of the object, and also its contents. The process of communicating between objects and transferring them over anover application boundaries is known as marshalling. Objects are converted intoremote objects when they derive from MarshalByRefObject. Then, when a clientactivates the remote object, it interfaces with a proxy for the remote object, as illus-trated in Figure 3.2. The proxy object acts on behalf of the remote object, and, aspreviously mentioned, is created when the client actives a remote object. Its mainW.Buchanan Unit 3 - .NET Remoting 3
    • objective is to make sure that all the messages sent to the remote object are sent tothe correct instance of the object. Client application domain Server application domain Client object Remoteable object (object.dll) ShowCapital() Proxy Remoting Channel Remoting System System Serialisation Figure 3.2: .NET remotingOn the remote machine, the remote object is initially registered into an applicationdomain. The MarshalByRefObject is then used to encapsulate all the informationrequired to locate and access the remote object, such as its class name, its class hier-archy, its interfaces and its communication channels. Activation occurs using theURL, and identifies the URI (Unique Reference Identifier) of the remote object. A MBR (Marshal-by-reference) always resides on the server, and the methods areexecuted on the server, while the client communicates with the local proxy. The fol-lowing shows an example of the ShowCapital class which derives from theMashalByRefObject, and contains a show() method. public class ShowCapital : MarshalByRefObject { public ShowCapital() Derive from { } MarshalByRefObject public string show(string country) { } }The MarshalByValue (MBV) involves serializing values on the server, and sendingthem to the client. An MBV object is declared by a class with the Serializable attrib-ute, such as:[Serializable()]public class NewMBVObject{}W.Buchanan Unit 3 - .NET Remoting 4
    • 3.4.1 ChannelsRemote objects transfer messages between themselves using channels. These chan-nels are thus used to send and receive objects, as well as sending information on themethods that require to be called. Each object must have at least one channel set upfor this communication, and the channel must be registered before a remote object iscalled. Once the object is deleted, the channel which it uses is also deleted. Also thesame channel cannot be used by different application domains on the same ma-chine. These channels map onto TCP port numbers, and the application must besure that it does not use one which is currently being used.3.4.2 HTTP and TCP channelsMessages which are transferred by the SOAP protocol use an HTTP channel,whereas a TCP channel uses a binary format to serialize all message. In the HTTPchannel, all the messages are converted into an XML format, and serialised (alongwith the required SOAP headers). The namespaces are:System.Runtime.Remoting.Channels.HTTP for HTTPSystem.Runtime.Remoting.Channels.TCP for TCPFor example to create a client connection to a server port of 1234: TcpChannel channel = new TcpChannel(1234); ChannelServices.RegisterChannel(channel);The HTTPChannel can be used for a wide range of services which are hosted by aWeb server (such as IIS). It has security built into it, but has an overhead of extrainformation (as it works at a higher level than TCP). The TCPChannel is more effi-cient in its operation, but does not have any security built into it.3.4.3 ActivationA key element of the .NET remoting framework is that it supports the activation ofremote objects as either a client or a server. Server activation is typically used whenremote objects do not required to maintain their state between method calls, orwhere there are multiple clients who call methods on the same object instancewhere the object maintains its state between function calls. In a client-activated ob-ject, the client initiates the object and manages it for its lifetime. Remote objects have to be initially registered with the remoting framework be-fore the clients can use them. This is normally done when a hosting applicationstarts up and then registers one or more channels and one or more remote objects. Itthen waits until it is terminated. When the hosting application is terminated, the ob-jects and channels are deleted. For an object to be registered into the .NET remotingframework the following need to be set: Assembly name. This defines the assembly in which the class is contained in. Type name. This defines the data type of the remote object. Object URI. This is the indicator that clients use to locate the object.W.Buchanan Unit 3 - .NET Remoting 5
    •  Object mode. This defines the server activation, such as SingleCall or Singleton.Remote objects are registered using the RegisterWellKnownServiceType, by passingthe required parameters into the method, such as: RemotingConfiguration.RegisterWellKnownServiceType (typeof(newclass.ShowCapital), "ShowCapital1", WellKnownObjectMode.SingleCall);which defines a SingleCall remote object, and the ShowCapital object, which iswithin the newclass namespace. ShowCapital is thus the name of the object, wherethe ShowCapital1 is the object URI. It is also possible to store the parameters in a configuration file then using Con-figure with the required configuration file, such as: RemotingConfiguration.Configure("myconfig.config");where the configuration file could be in the form of:<?xml version="1.0" encoding="utf-8" ?><configuration> <system.runtime.remoting> <application> <service> <wellknown mode="Singleton" type="newclass.ShowCapital, newclass" objectUri="ShowCapital1" /> </service> <channels> <channel ref="tcp server" port="1234" /> </channels> </application> </system.runtime.remoting></configuration>This method has the advantage that it does not need to be compiled with the appli-cation, and can therefore be edited as required, and will be read in as required. Thusa change of parameters, such as a change of object name does not require a recom-pilation. Once registered, the remote object will not instantiate itself, as this requires theclient to initiate it, or call a method. This is achieved by a client which knows theURI of the remote object and by registering the channel it prefers using GetObject,such as: TcpClientChannel channel = new TcpClientChannel(); ChannelServices.RegisterChannel(channel); ShowCapital sh= (ShowCapital) Activator.GetObject(typeof(newclass.ShowCapital), "tcp://localhost:1234/ShowCapital1");where: “tcp://localhost:1234/ShowCapital1”. Specifies that the end point is ShowCapital using TCP port 1234.W.Buchanan Unit 3 - .NET Remoting 6
    • Along with this, the compiler requires type information about the ShowCapital classwhen this client code is compiled. This can be defined with one of the following: With a reference to the assembly where the ShowCapital class is stored. By splitting the remote object into an implementation and interface class and then use the interface as a reference when compiling the client. Using SOAPSUDS tool to extract metadata directly from the endpoint. SOAPSUDS connects to the endpoint, and extracts the metadata, and generates an assembly or souce code that is then used in the client compilation.Another method is RemotingConfiguration.RegisterWellKnownClientType( typeof(ShowCapital), "tcp://localhost:1234/ShowCapital");None of these calls actually initiates the remote object, as only a proxy is createdwhich will be used to contact the object. The connection is only made when amethod is called on the remote object. Once this happens, the remote frameworkextracts the URI, and initiates the required object, and forwards the requiredmethod to the object. If it is a SingleCall, the object is destroyed after the method hascompleted.3.5 Applying .NET RemotingThe following sections show a remote objects are initiated and then how they can beused to communicate between a client and a server.3.5.1 Creating a remotable classThe following steps shows how a remote class is created (Figure 3.3). These are:1. Create a new blank solution (named NetRemoting1).2. Add a new class library (for example, named newclass). Select Add New Pro- ject, then select Class Library, as illustrated in Figure 3.3.3. Add System.RunTime.Remoting.dll as a Reference (if required).4. Change the name of the class file to a new name (for example, ShowCapi- tal.cs).5. Add the following code: C# Code 3.1:using System;using System.Data;namespace newclass{ public class ShowCapital : MarshalByRefObject { public ShowCapital()W.Buchanan Unit 3 - .NET Remoting 7
    • { } public string show(string country) { if (country.ToLower() == "england") return ("London"); else if (country.ToLower() == "scotland") return ("Edinburgh"); else return ("Not known"); } }}and the results are shown in Figure 3.5. This produces a class named ShowCapital,which has a method of show(). This class, once built, produces a remotable class inthe form of a DLL file, which is placed in the binDebug folder. In this case it willcreate a DLL named newclass.dll, as this is the name of the namespace. Client application domain Server application domain Objects passed by reference or value for local objects. For Client object remote it is not Server object possible to pass by reference – they must be marshalled. Proxy Remoting Channel Remoting System System Serialisation Figure 3.3: Remotable class Figure 3.4: Adding a new classW.Buchanan Unit 3 - .NET Remoting 8
    • Figure 3.5: Completed example3.5.2 Create a server-activated objectThis section shows how an application can be created which activates the remotableobject. As long as the application runs, the remotable object can be called by a client,and invoked.1. Add a New Project, and select Console Application, and name it (for example newclass2, as shown in Figure 3.6).2. Next add the references to the first project (the DLL file), and to the Sys- tem.Runtime.Remoting (Figure 3.7).3. Next the following code can be added: C# Code 3.2:using System;using System.Runtime.Remoting;using System.Runtime.Remoting.Channels;using System.Runtime.Remoting.Channels.Tcp;namespace newclass2{ class Class1 { [STAThread] static void Main(string[] args) { TcpServerChannel channel = new TcpServerChannel(1234); ChannelServices.RegisterChannel(channel,false); RemotingConfiguration.RegisterWellKnownServiceType (typeof(newclass.ShowCapital), "ShowCapital", WellKnownObjectMode.SingleCall); Console.WriteLine("Starting..."); Console.ReadLine(); } }}W.Buchanan Unit 3 - .NET Remoting 9
    • Client application domain Server application domain Client object Server Remoteable object innovation (object.dll) ShowCapital() Proxy Channel=1234 Remoting Channel Remoting System System Server-activation object Figure 3.6: Server-activation object (SAO)For this:RemotingConfiguration.RegisterWellKnownServiceType (typeof(newclass.ShowCapital), "ShowCapital", WellKnownObjectMode.SingleCall);defines a SingleCall activation mode (which means it will run once and then be de-leted), on the ShowCapital object, which is within the newclass namespace.ShowCapital is thus the name of the object, where the ShowCapital1 is the objectURI. This refers to a DLL file named after the namespace (in this case newclass.dll).The channel used is 1234. Once the server-activated component has been started itwill wait for the client to connect to it. As it is a SingleCall it will call the remote ob-ject once, and then it will be deleted. Thus every time it is called, it will notremember the previous state. If the Singleton option is used the remote object willstay active and will thus store its state. Figure 3.7: .NET remotingW.Buchanan Unit 3 - .NET Remoting 10
    • Figure 3.8: .NET remoting referencing3.5.3 Instantiating and invoking a server-activated objectThis section shows how an application can invoke a server-activated object. Thisruns on the client and calls the server to invoke the remotable class. The main stepsare:1. Add a New Project to the solution, using a Windows Application (Figure 3.9).2. Next a reference is added for a the System.Runtime.Remoting assembly (Fig- ure 3.10) and the remotable class (newclass), as shown in Figure 3.11. Client application domain Server application domain Client object Server Remoteable object innovation (object.dll) ShowCapital() Proxy Channel=1234 Remoting Channel Remoting System System Server-activation object Figure 3.9: Server invocationW.Buchanan Unit 3 - .NET Remoting 11
    • Figure 3.10: .NET remoting Figure 3.11: .NET remoting3. Add the following code: C# Code 3.3:using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Text;using System.Windows.Forms;using System.Runtime.Remoting;using System.Runtime.Remoting.Channels;using System.Runtime.Remoting.Channels.Tcp;using newclass;namespace WindowsFormsApplication1W.Buchanan Unit 3 - .NET Remoting 12
    • { public partial class Form1 : Form { public Form1() { InitializeComponent(); } ShowCapital sh; private void button1_Click(object sender, System.EventArgs e) { string country, cap; country = textBox1.Text; cap = sh.show(country); textBox2.Text = cap; } private void Form1_Load(object sender, System.EventArgs e) { TcpClientChannel channel = new TcpClientChannel(); ChannelServices.RegisterChannel(channel,false); RemotingConfiguration.RegisterWellKnownClientType( typeof(ShowCapital),"tcp://localhost:1234/ShowCapital"); sh = new ShowCapital(); } }}This then connects to server (in this case, with localhost, which has the IP address of127.0.0.1), using TCP port of 1234.3.5.4 Creating a control executableIt is possible to create an orderly start for the project, by selecting the properties ofthe solution, and then selecting Multiple Startup Project. This can then be used tocreate an orderly innovation of the programs, as the server must be started beforethe client. Obviously the remotable class will not be started-up, thus its action isNone, as illustrated in Figure 3.12. A sample run is given in Figure 3.13. Figure 3.12: .NET remotingW.Buchanan Unit 3 - .NET Remoting 13
    • Figure 3.13: .NET remotingW.Buchanan Unit 3 - .NET Remoting 14
    • 3.6 Tutorial 1Tutorial (Part 1): [Link]Q3.1 Implement the code in C# Code 3.1, C# Code 3.2 and C# Code 3.3, and prove that the application works. Next, complete the following:Tutorial (Part 2): [Link] (a) Add a debug message within C# Code 3.1 so that it displays the country which is being searched for.Tutorial (Part 3): [Link] (b) Add a counter within C# Code 3.1 so that the remoteable object returns a counter to show the number of times it has been called (as illustrated in Figure 3.14). Show thus, for the SingleCall that the counter will always show the same value. (c) Next modify C# Code 3.2, so that is uses the Singleton method, and show that the counter will increment for every access.Tutorial (Part 4): [Link] (d) Modify the application so that it uses HTTP rather than TCP. Figure 3.14: ExampleQ3.2 Contact a neighbour in the lab, and ask them to place your server compo- nent (dll and exe) from Tutorial Q3.1 onto their machine. Ask them to runW.Buchanan Unit 3 - .NET Remoting 15
    • the server component. Next run the Windows program to contact their server component, and prove that it works. Note: Make sure you use the IP address of your neighbour’s PC.Q3.3 Modify the server C# Code 3.2 so that it listens on port 80 (or any other re- served ports), and, if you have a WWW server running on your machine, prove that the error message is:An unhandled exception of type System.Net.Sockets.SocketException occurredin system.runtime.remoting.dllAdditional information: Only one usage of each socket address (proto-col/network address/port) is normally permittedQ3.3 From the Command Prompt, run netstat -a, and determine the TCP server ports which are open. Next run netstat -a -v, and observe the output. What does the address identify?Q3.4 Create a program which uses .NET remoting to implement the following: (a) Returns the IP address for a specified domain name. An example is given in Figure 3.15. Note, to get the IP addresses the following can be used: if (strHostName=="") strHostName = Dns.GetHostName(); IPHostEntry ipEntry = Dns.GetHostByName(strHostName); IPAddress [] addr = ipEntry.AddressList; Where the first IP address can be return (addr[0]). (b) Created another method which returns the hostname for a given IP address. Figure 3.15: ExampleW.Buchanan Unit 3 - .NET Remoting 16
    • 3.6.1 Client-activated objectThe lifetime of server-activated objects (SAO) is directly controlled by the server,whereas the lifetime of client-activated objects (CAO) is controlled by the callingapplication program, just as if it were local to the client.An SAO the remotable object is defined with: RemotingConfiguration.RegisterWellKnownServiceType (typeof(newclass.ShowCapital), "ShowCapital", WellKnownObjectMode.SingleCall);A CAO the remotable object is defined with: RemotingConfiguration.RegisterActivatedServiceType (typeof(newclass.ShowCapital));When initiating and invoking a SAO: RemotingConfiguration.RegisterWellKnownClientType( typeof(ShowCapital), "tcp://localhost:1234/ShowCapital");When initiating and invoking a CAO: RemoteConfiguration.RegisterActivedClientType (typeof(newclass.ShowCapital),”tcp://localhost:1234”);3.6.2 Tutorial 2Q3.5 Modify Tutorial Q3.1 so that it uses CAO instead of SAO.Q3.6 Modify Tutorial Q3.2 so that it uses CAO instead of SAO.Q3.7 Implement a remote object which has the following methods: Square(x). Which determines the square of a number. SquareRoot(x). Which determines the square root of a number. Power(x,n). Which determines the power of a number (x) raised to another number (n).W.Buchanan Unit 3 - .NET Remoting 17
    • 3.7 Configuration Files for remotingIn the previous examples the channel and the definitions for the remote object havebeen defined within the program (programmatic configuration). Thus it is not pos-sible to change them once the application has been compiled. An enhanced methodwhich allows the channel and remote object definition to be defined as an externalconfiguration is to use an XML file to define the parameters used in .NET remoting(declarative configuration). This is achieved either at a machine-level with the ma-chine.config file (which can be found in the config folder), or at an application levelwith an application configuration file. In an ASP.NET application the name of theconfiguration file is web.config. The general format is:<configuration> <system.runtime.remoting> <application> <lifetime> </lifetime> <service> <wellknown/> <activated/> </service> <client> <wellknown/> <activated/> </client> <channels> </channels> </application> </system.runtime.remoting></configuration>It includes the full name of the application, with a .config extension. Thus an appli-cation named myapp.exe will have an associated configuration file ofmyapp.exe.config.3.7.1 Register server-activated object with configuration fileRemotingConfiguration.Configure is used to register a server-activated object, suchas: static void Main(string[] args) { RemotingConfiguration.Configure("..//..//dotnetremote1.exe.config"); Console.WriteLine("Starting..."); Console.ReadLine();The file dotnetexample1.exe.config:<?xml version="1.0" encoding="utf-8" ?><configuration> <system.runtime.remoting> <application> <service> <wellknown mode="Singleton" type="newclass.ShowCapital, newclass" objectUri="ShowCapital1" /> </service> <channels> <channel ref="tcp server" port="1234" /> </channels> </application> </system.runtime.remoting></configuration>W.Buchanan Unit 3 - .NET Remoting 18
    • This achieves the same as: RemotingConfiguration.RegisterWellKnownServiceType (typeof(newclass.ShowCapital), "ShowCapital1", WellKnownObjectMode.Singleton);which defines a Singleton remote activation, and the ShowCapital object, which iswithin the newclass namespace. ShowCapital is thus the name of the object, wherethe ShowCapital1 is the object URI.3.7.2 Register client-side configurationThe client-side configuration is similar, but uses the <client> element. An example ofthe configuration file is:<?xml version="1.0" encoding="utf-8" ?><configuration> <system.runtime.remoting> <application> <client> <wellknown type="newclass.ShowCapital, newclass" url="tcp://localhost:1234/ShowCapital" /> </client> </application> </system.runtime.remoting></configuration>and for the call: private void Form1_Load(object sender, System.EventArgs e) { RemotingConfiguration.Configure("app2.config"); sh= new ShowCapital(); }Figure 3.16 shows an example of the output. Figure 3.16: .NET remotingW.Buchanan Unit 3 - .NET Remoting 19
    • 3.7.3 Tutorial 3Q3.8 Modify C# Code 3.1, C# Code 3.2 and C# Code 3.3, so that they use an XML configuration file for their remoting parameters. (a) Set one port to 1234, and the other to 9999. Prove that the program will create an exception. (b) Next, change both ports to 9999, and prove that the system works.Q3.9 Run the program, and from the command prompt, run netstat, and deter- mine that a TCP connection has been made. Outline its details:Q3.10 Set up the client and server to communicate on port 5555 (using the con- figuration file). Next, contact a neighbour in the lab, and ask them to place your server component (dll and exe) onto their machine. Ask them to run the server component, and run the windows program to contact their com- ponent, and prove that it works. Note: Make sure you use the IP address of your neighbours PC. Next, ask your neighbour to change the port to 8888 on the server side, and change the port on your machine. Prove that the system can still communi- cate.W.Buchanan Unit 3 - .NET Remoting 20
    • 3.8 Interface assemblies to compile remote clientsAn interface is an alternative method of creating an abstract class, and it does notcontain any implementation of the methods, at all. It provides a base class for all thederived classes. This is useful in hiding the code from other developers, as, in theprevious examples, the assembly to the remotable class has been included in the cli-ents project. In the following an interface named IDCapital is created, which has amethod of show(): C# Code 3.4:using System;namespace IDCapital{ public interface IDCap { string show(string str); }}This is the interface assembly. Next we can define the remotable object which im-plements the interface assembly: C# Code 3.5:using System;using System.Data;using IDCapital;namespace newclass{ public class ShowCapital : MarshalByRefObject, IDCapital.IDCap { public string show(string country) { if (country.ToLower()=="england") return("London"); else if (country.ToLower()=="scotland") return("Edinburgh"); else return("Not known"); } }}After which a remoting server can be created to register the remotable object thatimplements an interface assembly: C# Code 3.6:using System;using System.Runtime.Remoting;using System.Runtime.Remoting.Channels;using System.Runtime.Remoting.Channels.Tcp;using IDCapital;namespace newclass2{ class Class1 { [STAThread]W.Buchanan Unit 3 - .NET Remoting 21
    • static void Main(string[] args) { TcpServerChannel channel = new TcpServerChannel(1234); ChannelServices.RegisterChannel(channel); RemotingConfiguration.RegisterWellKnownServiceType (typeof(newclass.ShowCapital), "ShowCapital", WellKnownObjectMode.SingleCall); Console.WriteLine("Starting..."); Console.ReadLine(); } }}Finally a remote client is created which invokes the remotable object that imple-ments the interface assembly: C# Code 3.7:. . . IDCap sh; private void button1_Click(object sender, System.EventArgs e) { string country,cap; country=textBox1.Text; cap=sh.show(country); textBox2.Text= cap; } private void Form1_Load(object sender, System.EventArgs e) { TcpClientChannel channel = new TcpClientChannel(); ChannelServices.RegisterChannel(channel); sh= (IDCapital.IDCap) Activator.GetObject(typeof(IDCap), "tcp://localhost:1234/ShowCapital"); }The references are added as defined in Figure 3.17. Figure 3.17: .NET remotingW.Buchanan Unit 3 - .NET Remoting 22
    • 3.8.1 Soapsuds Tool for Interface Assembly GenerationAnother method which can be used to generate an interface assembly rather thanthe implementation assembly is to use the Soapsuds tool. For this the tool requiresthe URL of the remotable object, of which Soapsuds automatically generates the in-terface assemblies. An example, based on the previous sections is:soapsuds -url:http://localhost:1234/ShowCapital?wsdl -oa:newclass.dll -nowpwhich uses the required URL, and generates a DLL named newclass.dll. For exam-ple:> soapsuds -url:http://localhost:1234/ShowCapital?wsdl -oa:newclass.dll -nowpand listing the directory gives:>dir15/01/2005 21:20 1,078 App.ico15/01/2005 21:20 2,426 AssemblyInfo.cs16/01/2005 18:11 <DIR> bin16/01/2005 17:55 732 Class1.cs16/01/2005 18:38 3,584 newclass.dll16/01/2005 17:56 4,737 newclass2.csproj16/01/2005 18:27 1,803 newclass2.csproj.user16/01/2005 17:16 <DIR> objThe references are then added as Figure 3.18 and Figure 3.19. Figure 3.18: DLLW.Buchanan Unit 3 - .NET Remoting 23
    • Figure 3.19: References3.8.2 Tutorial 4Q3.11 Modify C# Code 3.1, C# Code 3.2 and C# Code 3.3, so it uses an interface assembly.W.Buchanan Unit 3 - .NET Remoting 24